be good at后+什么词

good at doing something.
good at playing basketball.
good at singing.

一般是动名词。

动名词，即动词的名词形式，通常是加ing.

名词、动名词

动名词doing be good at doing something
擅长做什么事情

be good at something 嘛，固定词组～所以后面跟的是名词喽。